System for maintaining a predetermined temperature at a given locus



Jan. 25, 1966 J. E. LINDBERG, JR 3,231,336 SYSTEM FOR MAINTAINING A PREDETERMINED TEMPERATURE AT A GIVEN LOCUS Original Filed Nov. 8, 1957 PRESSURE fr- REGULATOR T l I $0DIUM I I. J ELEMENT (263 5/ 50 I 152 k If i 54 TEMPERATURE SEMS 0R REA CT/OIV HYDROGEN f v55 SH RESfRVa/R i RES/STANCE I SEA/50R 56 I I T E COMPRESSOR 5 H5 4 REJt-R- 6/ 6 I VOIR j INVENTOR.

ATTOR NEY United States Patent 3,231,336 SYSTEM FOR MAINTAINING A PREDETERMINED TEMPERATURE AT A GIVEN LUCUS John E. Lindherg, Jr., 1170 Oleander Drive, Lafayette, Calif.

Original application Nov. 8, 1957, Ser. No. 695,357, now Patent No. 3,075,361, dated Jan. 29, 1963. Divided and this application July 3, 1961, Ser. No. 130,447

2 Claims. (Cl. 23-460) This application is a division of copending application Serial No. 695,357 filed Nov. 8, 1957, which issued on Jan. 29, 1963 as Patent No. 3,075,361.

This invention relates to a temperature control system for maintaining a predetermined temperature at a given locus.

Conventional heat transfer methods depend almost solely on the product of the specific heat and the quantity of a heat transfer medium that is cycled between the source and the sink. For example, when water is used to cool an engine, the amount of heat removed from the engine by the water is the product of the difierence in temperature between the engine and the air, the mass of water circulated, and the specific heat of water. While this method has its advantages and is satisfactory for many purposes, it also has many disadvantages, and in some circumstances they outweigh the advantages. Thus, some temperature ranges are too hot for use of liquid water, and even steam becomes very difficult to handle. In fact, it is well known that some atomic energy installations use liquid sodium in spite of its relatively low specific heat (about .294). The liquid sodium, considered abstractly, is less than one-third as efiicient as water, but water cannot be used in the liquid state above 100 C., and the liquid sodium is preferred to most other materials because its specific heat is high in comparison with most other metals.

When practicing the conventional methods of heat transfer, it is necessary to move the entire medium from the source to the sink. A relatively low amount of heat is transferred per quantity of medium moved. Moreover, large-capacity pumps have to be used if large amounts of heat are to be transferred.

The present invention differs from the prior art by placing substantial reliance on the heat energy associated with certain types of thermodynamic transformations, particularly those accompanying chemical reaction and physical solution. In some transformations, the energy change is orders of magnitude larger than that involved in heating conventional heat exchanger media. When considered in terms of the heat energy transferred per unit mass of medium moved, the present invention achieves rather astounding results.

Two requirements of my invention are: (1) In the thermodynamic transformation, heat must be absorbed from the source and released to the sink; (2) in a cyclic system, the transformation must be reversible between the temperature of the source and the temperature of the sink.

Many chemical compounds and solutions do not produc enough heat during their formation or dissolution to be of practical use in my invention. Moreover, many transformations are not reversible within practical ranges of temperature. The present specification therefore considers certain transformations that are reversible within practical temperature ranges and that absorb much heat per unit weight from the source and release it to the sink.

The method of this invention makes it possible to ab- 3,231,336 Patented Jan. 25, 1966 sorb a large proportion, in some cases the major portion, of the heat energy produced at the source in an endothermic transformation and to liberate that heat at the sink in an exothermic transformation. For example, hydrogen or oxygen may be liberated from certain metals at the source and recombined at the sink. In some instances, if desired, the temperature at the source may be the same as, or even lower than, the temperature at the sink; this invention enables the transfer of large quantities of heat in spite of a small temperature difference, and even in opposition to the temperature difference. When methods which rely upon specific heat alone are used, heat transfer between a source and a sink with but a small temperature differential is very inefficient; such methods cannot be used at all when the source is at a temperature lower than or equal to that of the sink. Even with the source temperature above that of sink, such methods allow little heat to be carried per unit weight of medium. But in the present invention, a highly endothermic transformation at the heat source can be used to transfer a rather vast amount of heat to the sink, even though the source and the sink are at the same temperature, or even if the source is at a lower temperature than the sink.

In this invention, the amount of heat Q which may be transferred by the heat-exchange medium of mass M may be expressed as:

Where Q is the heat of formation of the compound, S is the specific heat content of the compound, M is its mass, and Tsource and Tsink are the respective temperatures of the source and the sink. For heat to be trans ferred from the source to the sink, Q must be a positive quantity, which in turn implies that Q must be greater than c source' sink) if sink source- This l ment for heat tranfer from source to sink can usually be met by a proper choice of the heat-exchange medium according to the present invention, for while S is a relatively small quantity, Q is quite large for many materials employed in this invention, as is shown in several I examples on following pages. In the conventional style of heat transfer, however, the term Q is absent in the above expression and such methods would fail if sink source since in that event heat would be carried from the sink to the source. Since Q is large for many reactions, the present invention will operate at superior efficiency over very wide temperature ranges, including the case of the source temperature being considerably lower than that of the sink.

Another important advantage of the invention is that often only a part, frequently a small part, of the medium need be transferred between the source and the sink. Instead of having to pump the entire mass, only a small fraction is pumped. For example, in certain applications where a metallic hydride is used, only the hydrogen need be transferred. In certain particular reactions explained below, a tremendous amount of heat energy can be transferred per unit mass of the hydrogen pumped.

There are other advantages of the invention. For example, the time-temperature relationship at the sink can be controlled independently of the time-temperature input at the source by controlling the rate of the recombination of a gas and a metal at the sink.

The present invention also distinguishes from the prior art in being practical at very high temperatures. Heat can be transferred at temperatures not heretofore feasible, and this fact demonstrates the utility of this invention in chemical, petroleum, metal-processing, and atomic energy applications, among others.

Other objects and advantages of the invention will appear from the following description of several preferred embodiments thereof.

The drawing is a schematic diagram of a heat-transfer system embodying the invention in which there is a control by pressure variation.

Some particular thermodynamic transformations embodying the invention have been found to be exceptionally useful, and they will serve as examples illustrating the principles of this invention. These transformations concern the interaction between certain gases and certain metals.

Hydrogen combines with some metals to produce actual stoichiometric hydrides. With some other metals it forms what are often called hydrides but are not stoichiometric compounds; actually the hydrogen is physically dissolved in these metals. Except for careful chemical investigation, it would be diflicult to tell the difference between the solutions and the true reactions; in fact, only recently has there been any differentiation. In both cases considerable heat is produced during combination (exothermic), and in both cases heat is required for dissolution (endothermic). Both produced hydrides, and the principal difference is only that in one case reaction is stoichiometric and in the other it is not. Both reactions are reversible; both release heat as hydrogen is taken into the metal due to temperature decrease or pressure increase or both, and both absorb heat when the hydrogen is removed from the metal due to decrease in pressure or increase in hydride temperature or both.

The stoichiometric reaction is between hydrogen and the alkali and alkaline earth metals. Specifically, hydrogen reacts with lithium, sodium, potassium, rubidium, cesium, calcium, radium, strontium, cfranoium and barium; in stoichiometric proportions to form hydrides. The heats of formation and dissolution of all these hydrides is quite large, of the order of 10,000 calories per mole. Moreover, the ranges of temperatures between formation and dissolution are quite practical for use in many applications of heat exchange. Some specific examples are given below, and Tables I and H are furnished to show some of the heat properties of some of these compounds.

Norm-In this and in the following tables, the following relations hold true:

Mm (1) Sm=Cm- A i cp t,

(3) Sc=Sm+Sg Where:

My is the formula mass of the gas,

Mm is the formula mass of the metal,

Me is the formula mass of the hydride,

Cm is the specific heat of the metal (gram calories per gram per degree eentigrade), and

Cp is the specific heat of the gas at constant pressure. (For II; this is 3.50 over the 1,000 0. range.)

Hydrogen interacts with two other groups of metals, one of these, known as the Group A metals, consists of copper, silver, molybdenum, tungsten, iron, cobalt, nickel, aluminum, platinum, manganese, technetium, rhenium, osmium, iridium, ruthenium, and rhodium; chromium is a member of this group at temperatures greater than about 300 C. The action appears to be a type of solubility, and the solubility increases with increasing temperature. However, a relatively small magnitude of heat is absorbed as the temperature is raised and hydrogen goes into solution in the metal. This heat is liberated when the temperature or pressure is decreased to cause removal of the gas from the metal.

The solubility of hydrogen in the Group A metals varies (at least over a wide range of temperatures and pressures) according to the equation:

in which s is the solubility of molecular hydrogen in the metal, 0 is a constant of proportionality,

P is the pressure,

e is the base of natural logarithms,

Q is the heat absorbed in calories per mole. of H d is the density of the metal, and

T is. the temperature, in degrees Kelvin.

More useful is the solution of hydrogen in what are known as the Group B metals, the class consisting of scandium, titanium, vanadium, ytterbium, zirconium, niobium, hafnium, tantalum, the rare earth metals (atomic numbers 57 through 71), and the actinide metals (atomic numbers 89 through 103); palladium is a member of this group at temperatures greater than about 300 C. This solution is often termed a hydride, though it is not a stoichiometric compound. The solubility of hydrogen in Group B metals varies (at least over a wide range of temperatures and pressures) according to the equation:

8 Pl/2 +Q/l.987T s s T where s is the solubility at saturation at room temperature,

0 is another constant of proportionality, and s, P, e, Q, and T have the same meaning as in the preceding equation.

Some of the heat properties of some of these hydrides are shown in Table III.

Table III .H eat properties of certain Group B hydrides [The units in the table headings are the same as in Table I] Heat of Heat Content Heat Content Heat Content Hydride Formation of Metal of Gas of Hydride Sm Sg Sc vessel at a constant temperature.

usually achieved by providing separate heating and cooling devices and using one or the other of these in response to a temperature sensor.

However, equivalent results may be obtained more conveniently and more economically by the single system illustrated diagrammatically in the drawing. Here a reaction vessel 50 is provided With an element 51 containing a suitable hydride-forming metal which, for purposes of this example, may be sodium. There are a temperature sensor 52 and a resistance sensor 53 at the sodium element 51, the sensors 52 and 53 being connected respectively to control means 54 and 55 by some suitable arrangement. The element 51 is connected to a reservoir 56 of hydrogen gas by two links, one of them a valve line 57 containing a valve 58 and a pressure-reducing regulator 59 and the other a valved line 60 containing a valve 61 and a gas compressor 62.

Suppose that the sodium has been partially converted to sodium hydride. Also suppose that it is desired to maintain the reaction vessel 50 at a temperature of 421 C. By calculation from the dissociation pressure against the temperature relation, it will be found that the control element 51 will be in equilibrium at this temperature it the hydrogen pressure thereover is maintained at one atmosphere pressure (760 mm. mercury). If it is desired to add or remove heat from the element 51, it is only necessary to change the pressure of gas over the solid material 51 by means of the pressure regulator 59 or the compressor 62. If the temperature of the reaction vessel 50 becomes lower than desired, the greater heat thus required in element 51 is produced there by causing hydrogen gas to flow into the element from the hydrogen reservoir 56 through the pressure regulator 59. Conversely, if the temperature of the reaction vessel 50 becomes higher than desired, the surplus heat in the element 51 is removed by removing hydrogen gas therefrom by means of the compressor 62. Any change in temperature at the reaction vessel 50 can be transmitted by the temperature sensor 52 to its control 54, where a signal is generated in a wellknown manner to afiect the pressure regulator 59 or the compressor 62 in the appropriate manner.

Since the element 51 cannot provide heat for or remove heat from the reaction vessel 50 in indefinite amounts, a conventional heat exchanger 63 may be installed at the element 51 to transfer heat to or from a heat reservoir 64 as needed.

It has been observed experimentally that the electrical resistance of a hydride, such as the sodium hydride in this example, is directly proportional to the amount of hydrogen adsorbed in the hydride: i.e., resistance is proportional to degree of ingassing of the hydride. It means are provided to measure this resistance at the element 51, then an increase in heat demand by the reaction vessel 50 will cause an increase in the degree of ingassing of the element 51 and a consequent increase in resistance thereof, as measured by the sensor 53, which might typically take the form of a Wheatstone bridge, providing a signal to its control 55. A decrease in heat demand by the reaction vessel 50 would cause a decrease in the degree of ingassing of the element 51 and hence a decrease in the resistance measured by the sensor 53. The control 55, responding to a decrease of hydride resistance as sensed by the sensor 53, causes heat to be removed from the element 51 through the heat exchanger 63, delivering the removed heat to the heat reservoir 64. An increase of hydride resistance as sensed by the sensor 53 causes heat to flow from the reservoir 64 through the heat exchanger 63 to the element 51, again under control of the control means 55. Control of heat flow to or from the reservoir 64 is effected in a manner that maintains the average resistance of the hydride as sensed by the sensor 53 to be that corresponding to the desired equilibrium or mean value of degree of hydride ingassing. Thus, removal of hydrogen from or its addition to the element 51 is used to quickly and accurately con- 2Na +H NaH is given by the equation log P=11.66- T where P is pressure in millimeters of mercury and T is temperature in degrees Kelvin.

To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

For example, although all of the examples given above use only single-metal hydrides and oxides, it should be noted that mixtures or alloys of suitable metals may be used. Alloying techniques oifer :a number of advantages. For one thing, the quantity of hydrogen that may be contained in an alloy may be larger than the quantity contained by equivalent amounts of the separate metals. For another, the transition temperatures of the pure metals may be modified by the addition of small quantities of alloying metals. For yet another, some alloys may be more convenient to handle than the constituent metals. In particular, lithium might be handled as a solid at high temperatures by alloying it with more refractory alkali metals.

What is claimed is:

1. A system for maintaining a predetermined temperature at -a given locus, comprising a reaction vessel at said locus, metal in said vessel of the type that combines exothermically with hydrogen to form a hydride, said metal remaining in said vessel throughout operation of said system, a supply of hydrogen, valve means for admitting a controlled flow of hydrogen from said supply into said vessel at desired times and for changing said flow at other desired times and for stopping said how at still other desired times, the admission of said hydrogen increasing the pressure in said reaction vessel and thereby raising the temperature of said metal due to the exothermic combination of said metal with said hydrogen, pumping means for extracting hydrogen from said vessel, thereby lowering the pressure and temperature of said reaction vessel, temperature sensing means at said locus, and control means actuated by said sensing means for actuating each of said valve means and said pumping means according to whether the temperature at said sensing means is higher or lower than said predetermined temperature.

2. A temperature control system comprising a reaction vessel, metal remaining in said vessel throughout operation of said system, said metal being of a type that combines exothermically with hydrogen to form a metal hydride, a hydrogen reservoir, supply means for supplying hydrogen from said reservoir to said vessel, exhaust means for withdrawing hydrogen from said vessel and conveying it to said reservoir, a resistance sensor actuated by the electrical resistance of the metal and such hydride as is formed by the combination of said metal with said hydrogen in said vessel, and control means actuated by said sensor to con-trol each of said supply means and said exhaust means in response to the change in resistance caused 'by the amount of hydrogen present in said vessel, so as -to admit further hydrogen while retaining the hydrogen already in the vessel or to withdraw hydrogen while cutting oif further supply to said vessel, depending on the value of said re- 7 8 sistance, and thereby to change the temperature at said 1,923,865 8/1933 Handforth. vessel. 2,541,857 2/1951 Besselman et a1. 32465 X 2,864,761 12/1958 DOuville et a1. 23204 X References Cited by the Examiner 1,450,023 3/1923 Edelman 23-253 X JAMES TAYMAN, Examiner- 1,790,369 1/1931 Downs. 

1. A SYSTEM FOR MAINTAINING A PREDETERMINED TEMPERATURE AT A GIVEN LOCUS, COMPRISING A REACTION VESSEL AT SAID LOCUS, METAL IN SAID VESSEL OF THE TYPE THAT COMBINES EXOTHERMICALLY WITH HYDROGEN TO FORM A HYDRIDE, SAID METAL REMAINING IN SAID VESSEL THROUGHOUT OPERATION OF SAID SYSTEM, A SUPPLY O HYDROGEN, VALVE MEANS FOR ADMITTING A CONTROLLED FLOW OF HYDROGEN FROM SID SUPPLY INTO SAID VESSEL AT DESIRED TIMES AND FOR CHANGING SAID FLOW AT OTHER DESIRED TIMES AND FOR STOPPING SAID FLOW AT STILL OTHER DESIRED TIMES, THE ADMISSION OF SAID HYDROGEN INCREASING THE PRESSURE IN SAID REACTION VESSEL AND THEREBY RAISING THE TEMPERATURE OF SAID METAL DUE TO THE EXOTHERMIC COMBINATION OF SAID METAL WITH SAID HYDROGEN, PUMPING MEANS FOR EXTRACTING HYDROGEN FROM SAID VESSEL, THEREBY LOWERING THE PRESSURE AND TEMPERATURE OF SAID REACTION VESSEL, TEMPERATURE SENSING MEANS AT SAID LOCUS, AND CONTROL MEANS ACTUATED BY SAID SENSING MEANS FOR ACTUATING EACH OF SAID VALVE MEANS AND SAID PUMPING MEANS ACCORDING TO WHETHER THE TEMPERATURE AT SAID SENSING MEANS IS HIGHER OR LOWER THAN SAID PREDETERMINED TEMPERATURE. 